Organic pigments typified by phthalocyanine and the like have properties including light resistance, heat resistance, migration resistance, vivid coloration, and superior color strength. When these types of organic pigments are used for coloring resins having partial crystallinity such as polyolefins and polyesters, the large nucleation effect of the pigment tends to effect the crystallinity, such as increasing the crystallization temperature of the resin having particle crystallinity and reducing the size of the spherulites, thus causing a phenomenon in which the shrinkage characteristics and/or the shrinkage balance (mold shrinkage, shrinkage difference) of the colored resin change. As a result, deformation such as distortions or dimensional variations has tended to appear in molded articles using resins having partial crystallinity, causing molding process problems. Deformation such as distortions can be a fatal problem for plastic molded articles such as containers, resin pallets, caps and bottles.
One method for reducing deformation such as distortions in plastic molded articles involves using a mold that takes account of dimensional variations caused by deformation such as distortions. However, because the shrinkage of the molded article varies considerably depending on the type of resin, the type of colorant, the type of additives and the molding conditions and the like, designing a mold that takes account of deformation is difficult, and numerous mold modifications must be performed. Mold manufacturers also attempt to reduce deformation by altering the process conditions such as the molding temperature, the injection pressure, the injection time, the injection rate and the cooling time and the like. But even in these cases, because the shrinkage of the molded article still varies depending on the type of resin, the type of colorant, the type of additives, and the size and shape of the molded article, setting process conditions that predict deformation is difficult, and numerous modifications of the process conditions by trial and error are typically required. Further, other problems arise in that the molding cycle lengthens, and the productivity deteriorates.
The addition of crystallization agents (crystal nucleating agents, nucleating agents or crystallization accelerators) is also used as a method for reducing deformation. In one such method, by adding a crystallization agent containing a large amount of a component that can function as a crystal nucleus, fine crystals can be formed uniformly and rapidly, and the effect of the pigment on shrinkage can be reduced, thereby reducing deformation. Alternatively, in another method, by adding a crystallization agent that causes shrinkage in a different direction from the direction of shrinkage caused by the pigment, any apparent shrinkage difference is eliminated, thereby reducing deformation. It is known that by using a crystallization agent, the molding cycle can be shortened, and the rigidity and transparency can be improved.
However, methods involving the addition of a crystallization agent still have an inadequate effect on mold distortions caused by organic pigments. Accordingly, the ideal method is to modify the pigment used as the colorant so that it does not act as a crystal nucleus. Examples of methods that have been used for modifying the pigment include methods in which the crystal form, the particle size or the shape of the pigment is altered, methods that use pigments having any of various substituents introduced into the pigment structure, methods for modifying the pigment surface by adding a pigment or a pigment derivative (organic dye derivative) having any of various substituents introduced into the pigment structure, and methods for modifying the pigment surface by subjecting the pigment to a surface treatment with a resin and/or silane coupling agent or the like.
Methods in which the crystal form, the particle size or the shape of the pigment is altered are disclosed in Patent Literature 1, Patent Literature 2 and Patent Literature 3. However, none of these methods yields an adequate effect. Further, there is a possibility that altering the crystal form, the particle size or the shape of the pigment may have an adverse effect on the original properties of the pigment such as the hue, dispersibility, color strength, heat resistance and light resistance.
Methods that use pigments having any of various substituents introduced into the pigment structure are disclosed in Non-Patent Literature 1 and Patent Literature 4. These methods involve introducing a prescribed number of halogens into a phthalocyanine structure. Although deformation is reduced in these methods, other problems arise, including a deterioration in properties such as the superior color strength and high vividness that the original phthalocyanine pigment displayed, and a large change in the hue.
Examples of methods for modifying the pigment surface by adding a pigment derivative (organic dye derivative) having any of various substituents introduced into the pigment structure include examples using phthalimidomethyl derivatives disclosed in Patent Literature 5 and Patent Literature 6. Although these methods enable some reduction in deformation, the effect is still inadequate, and another problem arises in that if the derivative is added in a large amount to reduce deformation, then the migration resistance tends to deteriorate.
Another example of a method for modifying the pigment surface by adding a pigment derivative (organic dye derivative) having any of various substituents introduced into the pigment structure is disclosed in Patent Literature 7. Patent Literature 7 discloses a mixture of a copper phthalocyanine pigment derivative, a halogenated phthalocyanine and phthalocyanine.